Worcs Brown Hairstreak Update

Well……what an eventful and exciting last few weeks it’s been in the world of the West Midlands Brown Hairstreak!

 The last six months had continued the fairly quiet trend that we had been experiencing since Summer 2015 with adult sightings in Grafton Wood, in 2016, well down on that previous summer. Once this winter’s egg searches then got underway in November, the similar theme continued. Counts at most sites that are monitored every year, were either down or about the same as the previous winter (which was, in itself, a disappointing one). Some sites bucked the trend though such as the National Grid site at Feckenham, which had the best count we’ve ever recorded there, responding to the great management work done by the Worcs Wildlife Trust and National Grid. Plus a long stretch of footpath hedgerow near Bishampton that we’re now using for the new BC Head Office monitoring methodology and where eggs were only found for the first time, a few years ago. Large numbers of eggs were found here this winter, easily surpassing last years’ total and seemingly indicating the build-up of a colony right at the southern edge of the known distribution of the butterfly in Worcs.

Events really started to take off though just before Christmas, with the discovery of what were the most southerly eggs ever found for this current-day Worcs population. These eggs were actually in an already recorded 1Km grid square but later that same day, after moving on to a nearby (previously unrecorded) square and searching there, Jenny Tonry discovered an egg on the northern outskirts of the village of Pinvin, in square SO9549.

A few weeks later, one of our regular Thursday searches had to be cancelled because of a bad weather forecast. Undeterred, two of us then went out searching (independently) the following day, in better weather, with the result that three more previously unrecorded squares were ticked off the list. These three squares were the ones flanking Tibberton village (SO9056/57/58) and were significant in that they’ve all been searched many times before in previous winters, to no avail. These squares were also out near the extreme western edge of the butterfly’s Worcs distribution. So again, these egg records provide compelling evidence of distribution expansion of the butterfly.

It was becoming increasingly clear, from all these ‘new square records’, that the Brown Hairstreak had experienced a flight season characterized by ‘dispersal’ and it was therefore going to be worth putting in a bit of extra effort to try and find other new square territories.

Cue a couple of weeks ago and the discovery of another new square record in yet another location that had been unsuccessfully searched in many previous winters. This one being on Pumphouse Lane, close to Redditch, in SP0166, and these discoveries marked the most northerly eggs so far found. This was then followed, just a week ago, by the discovery of an egg over the border in Warks, east of Astwood Bank plus  egg records in another new ‘Redditch’ square: SP0364 at Hunt End.

We had therefore, in just a single winter, recorded the most northerly and southerly eggs in the distribution, whilst also finding them out very close to both the western and eastern extremes!

With all this ‘edge of distribution’ exploration going on it might seem like there wouldn’t have been much time left to devote to our core area searches at Grafton Wood however, sandwiched in between all these new range discoveries, have been some incredible recent finds within the wood itself. Following a rather abortive attempt at searching some excellent areas of Blackthorn coppice and re-growth, in a much hampered heavy hoar frost search a few weeks previously, we decided to return to carry out a more systematic and painstaking search of some key areas within the wood. The result of these searches was that the in-wood total number of eggs found this winter at Grafton was a staggering 555. One particularly favourable ride corner revealing 186 eggs!

These searches within Grafton Wood itself have only been carried out over the last three winters, and are done to provide a monitoring and planning tool to aid the huge amount of excellent management work that has taken place within Grafton over the last few years to open up the wood and cut down old blackthorn thickets. The egg totals have proved beyond all doubt, how fantastically well the butterfly has responded to all this management work.

This brings the news of an exciting Brown Hairstreak season, right up-to-date although, at the time of writing, there’s still a few more weeks left for egg searching. So who knows what we may yet turn up, before the Blackthorn comes into flower and the 2017 egg searching season draws to a close?

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